Using the IRAM 30m millimeter radio telescope we mapped the line emission of the J=1-0 and J=2-1 transitions of 12C0, 13C0, and C180 in the nuclear region of the spiral galaxy IC342. This study demonstrates the value of multi line studies to investigate the neutral interstellar medium in extragalactic sources. Our observations as well as calculations of simple models of CO excitation and radiative transport show that the molecular gas in the nucleus is warm and that physical conditions vary with position in the galaxy. The molecular gas in the central kiloparsec of IC342 has a kinetic temperature of at least 30K and a molecular hydrogen density of about 3xl03 cm”3. At distances more than 500pc north and south of the center the kinetic temperature is significantly less (≥13K). About 500 pc north east of the center we find evidence for optically thin CO emission originating in a component of warm gas with a temperature of at least 40 K. Our model calculations result in conversion factors between the H2 column density and the 12CO (1-0) line intensity close to the value of 3–4×1020 cm-2/K km s-1 derived for molecular clouds in the Galaxy. The molecular mass contained in the central two kpc of IC342 is of the order of 2×108 M⊙.

CO(2→1) observations of a number of galaxies have recently been obtained with the CSO. Examples are presented here to illustrate the capabilities of the instrument.

A decade of galaxy observations at the Crawford Hill 7 m antenna are summarized. Significant results include the mapping of spiral arms in CO, the demonstration that gas in many spiral galaxies is roughly half atomic and half molecular, the detection of extragalactic HCO+, CS, 13CO and C18O, and the observation of molecular material in the halo of M82.

A large project of studying various transitions and isotopie species of CO in M82 has been carried out with the 30-m IRAM radio telescope. A 1.′6×1.′0 area was mapped in 12CO(2→1) with 13″ resolution (Loiseau et al., 1988a). The purpose of these observations was to obtain high signal-to-noise, high resolution data for comparison with the 12CO(1→0) observations of Nakai et al. (1987). A 13CO(2→1) observation covered the central 110×017 region (Loiseau et al., 1988b) and allowed to establish the velocity field of CO in the inner nuclear region. The position angle of the rotation axis of 13CO is aligned with the optical rotation and at some 30° relative to the 12CO velocity field. The 13CO map also shows the existence of clumped emission in the central region. All data show the rotating molecular ring. At some selected points (nucleus, major axis) 12CO/13CO ratios in both the (1→0) and (2-H) transition have been determined. The earlier suggestion that optical depth plays an important role in M82 has been confirmed. Variations of optical depth have been determined in the sources that there are several extended (>100pc) molecular complexes.

The study of molecular clouds in dwarf galaxies was, until recently, an arduous task and provided detections in only a handful of sources (see Thronson and Bally 1986; Wiklind et al. 1986; Tacconi and Young 1987; Arnoult et al. 1988). Line strengths observed in CO were small (<100mK) and measurements were confined to one position per source, thus inhibiting any detailed work. However, dwarf galaxies appear to be much more abundant than either spirals or large ellipticals and play an important role in our understanding of star and galaxy formation (see e.g. Gerola et al. 1980; Gallagher and Hunter 1984; Silk et al. 1987). With small rotational velocities (typically 50-lOOkms-1), the absence of density waves, and low metallicities, they provide, by "local" standards, an interstellar environment with even more extreme conditions than the outer Galaxy. Detailed molecular studies are hence important.

To determine the distribution of molecular gas in the Large and Small Magellanic Clouds (LMC and SMC), we made complete surveys in the J=1-0 transition of CO, of the central 6°×6° and 3°×2° areas of the LMC and SMC, respectively. The observations were made with the 1.2m Columbia Telescope at Cerro Tololo, which provides and angular resolution of 8.8 arcmin at 115 GHz. The spectral resolution of the surveys was 1.3 km s-1 and the sensitivity in antenna temperature was 0.05 K for the LMC and 0.02 K for the SMC.

During the last two years, observations of the molecular cloud content of early type galaxies have drastically changed our view of these systems as inert gas-poor galaxies with little or no star formation activity. Systematic surveys in the CO (J=1-0) line (Wiklind and Henkel, 1988a,b; Thronson, private communication) have shown that an IR selected sample of early type galaxies contains typically 107-108 Mo of molecular hydrogen gas. This is similar to the typical HI masses found in these galaxies (Knapp et al., 1985; Wardle and Knapp, 1986).

The majority of infrared active galaxies (ffir/fb ≥ 2) have molecular to atomic mass fractions in the range of 0.5 to 2.0. Among the galaxies with the higher infrared excesses there are spectacular cases of HI deficient systems, where less than 15% of the total mass of interstellar gas is in atomic form. The optical morphology of luminous infrared galaxies suggest that the overall mass fractions of molecular to atomic gas, and the infrared luminosities per nucleon of interstellar gas are enhanced during galaxy-galaxy interactions.

Recent high resolution interferometric observations of the molecular gas in luminous IR galaxies reveal extraordinary concentrations of star forming material in the central few kpc. In several of the nearest IR bright galaxies, the molecular gas in the central regions is concentrated in a bar-like distribution (IC342, NGC 6946, and NGC 253) and in NGC 1068, approximately 40% of the molecular gas is confined to two arms or a ring at approximately 1.6 kpc radius. Interferometry on the most luminous galaxies (LIR ≥ 1011L⊙) reveals that approximately half of the total interstellar matter is contained in the central kpc with mean densities of several hundred H2 cm-3. Such gas concentrations should result in the very rapid formation of stars, i.e. a central star burst yielding a massive central star cluster.

The Proceedings of these two meetings will be edited by G.. Cayrel de Strobel, M. Spite and T. Lloyd-Evans and published by the printing office of Paris Observatory.

We present here an overview of what has been discussed during these meetings.

An object of this meeting is to define and emphasize the best practices that allow stellar photometry done with array detectors to be as accurate as possible. We dream of applying simple and clearly justified principles; in reality, we find the equipment has physical and technical properties that interfere with each other. Photometry is a method, a metrology; so we first have to define the desired accuracy. Some will be happy with 0.1 magnitude; others need 0.01, or even 0.001 magnitude. The necessary precautions must be matched to these ambitions.

The search for high-quality, large-format CCD imagers during the 1980’s reminds me of a journey across a large and forbidding desert. One starts off full of great expectations of a quick completion, but discouragement sets in around mid-journey as the barrenness of the landscape becomes apparent and the goal on the horizon is shown to be only a mirage. Finally, mountains resolve themselves from the mirages and we take heart in knowing that we seem finally to be making some progress. I think the analogy fits the CCD situation well, starting with the view from the time period 1979–80 and working toward the present.

In the last few years, as the CCD cameras have been routinely used in most of the Observatories, there has been a growing concern among the scientific community about the major weakness of this very good detector: the format of the available chips is too small for many applications.

The Wide-Field and Planetary Camera (WF/PC) is a CCD imaging instrument which is part of the Hubble Space Telescope. Ground-based observations have been made with a CCD system similar to those of the WF/PC in order to establish the standard star sequence to be used for in-flight photometric calibration. Because the WF/PC passbands differ from those in previous photometric use, the filters and CCDs will define a new photometric system. We outline here the procedures used to establish the calibration fields to be used in flight (see Harris et al. 1988 for additional details).

There are many factors which make it difficult to relate instrumental CCD photometry to a fundamental standard system with an accuracy much better than about 1%. Here I will address only three of them: (1) infrared leaks in the filters; (2) the finite opening and closing times of mechanical shutters; and (3) changes in the air mass for long integrations. I will be approaching these subjects from the point of view of a visiting astronomer at someone else’s observatory, who gets three or four nights of observing time a year, and has only the afternoons preceding those nights to perform whatever tests can be carried out while the equipment sits on the telescope.

We briefly review some problems in the flatfielding of CCD images, in the context of three data-taking modes: stare, short scan, and drift scan. The principal sources of flatfielding imperfections are: (1) mismatch in the spectra of the astronomical sources of interest and the flatfield illumination; (2) a variety of low-level additive errors; and (3) nonlinearities of the CCD response. Residual flatfielding errors are probably the limiting factor in high-precision astronomical photometry. Flatfielding accuracies of the order of 1 – 2% per pixel are commonly achieved; with some effort, accuracies of ~ 0.1% can be reached; higher accuracies require a substantial effort, or improvements in the quality of CCD chips. In general, scanning data taking modes outperform the “standard” stare mode.

Methods have been developed for high precision photometry in crowded stellar fields. The procedure includes the following steps:

• • Determination of a two-dimensional point spread function

• • Definition of groups of stars with mutually overlapping images

• • Determination of local background for each star group

• • Simultaneous fitting of point spread functions, one for each star in the group

The Lund approach emphasizes interactivity. Many fundamental procedures are facilitated by the use of an optimised image display. Extensive modelling has been done to study the influence of various error sources.

The observed light distribution in long exposure star images (PSF) may be fitted equally well by a variety of models. But dealing with undersainpled star images, only the use of the multi-Gaussian model allows the correct model parameters estimation, taking into account integration on pixel surface, image off-centering and background behaviour. It is also shown that the convolution of a spherical source with the multi-Gaussian and Moffat’s models gives in practice the same result.

Astronomy being an observational science, it is clear that archiving must be an important part of our professional activities, because not preserving our observations means that we are building “on sand”.

This meeting was dedicated to Helen DODSON-PRINCE who has contributed so much to the field. Unfortunately, she was unable to attend the General Assembly, but a telegram has been approved by acclamations and sent to her, expressing to our colleague and friend the deep admiration and the friendly feelings of the solar community, as gathered in Baltimore.